In process automation technology, as well as manufacturing automation technology, field devices are often employed, which serve to register and/or influence process variables. For the registering of process variables, measuring devices are used, which, in each case, exhibit at least one sensor and one measurement transmitter. Such measuring devices include, for example, fill-level measuring devices, flow measuring devices, pressure and temperature measuring devices, pH-redox potential measuring devices, electrical conductivity measuring devices, etc., which ascertain the respective process variables, fill-level, flow, pressure, temperature, pH-value and conductivity. For influencing process variables, actuators are used, for example valves or pumps, via which the flow of a fluid in a section of pipeline or the fill-level in a container can be changed.
In principle, all devices, which are employed near to a process and which deliver or work with process-relevant information, are referred to as field devices. In addition to the aforementioned measuring devices/sensors and actuators, units that are directly connected to a fieldbus and which serve to communicate with superordinated units (e.g. remote I/Os, gateways, linking devices and wireless adapters) are also generally referred to as field devices. A large number of these devices are produced and sold by the Endress+Hauser Group.
In modern industrial facilities, field devices are, as a rule, connected with superordinated units via fieldbus systems (e.g. Profibus®, Foundation Fieldbus®, HART®, etc.). Normally, the superordinated units involve control systems or control units, for example a PLC (programmable logic controller). The superordinated units are used, for example, for process control, process visualizing, process monitoring, as well as in the start-up of the field devices. The measurement values registered by the field devices—especially from the sensors—are transmitted via the connected bus system to a superordinated unit, or, as the case may be, to several superordinated units. Additionally, a transfer of data from the superordinated unit to the field devices via the bus system is necessary; this is used especially in the configuring and parametering of field devices or for diagnostic purposes. Generally speaking, the field device is serviced from the superordinated unit via the bus system.
In addition to a hardwired data transmission between the field devices and the superordinated unit, the possibility of a wireless data transmission also exists. In particular, in the case of the bus systems, Profibus®, Foundation Fieldbus® and HART®, a wireless data transmission via radio is specified. Additionally, radio networks for sensors are more precisely specified in the standard IEEE 802.15.4. For the realization of a wireless transmission of data, field devices are designed, for example, as radio-field devices. As a rule, these exhibit a radio unit and an electrical current source as integral components. In such a case, the radio unit and the electrical current source can be provided for in the field device itself, or in a radio module permanently connected to the field device. Through the electrical current source, an autarkic energy supply for the field device is made possible.
Furthermore, there exists the possibility to upgrade field devices without radio units—i.e. the current installed base in the field—to radio-field devices through the attachment of a wireless adapter which features a radio unit. A corresponding wireless adapter is described, for example, in the publication WO 2005/103851 A1. The wireless adapter is, as a rule, connected to a fieldbus communication interface of the field device in a detachable manner. Via the fieldbus communication interface, the field device can transmit data over the bus system to the wireless adapter, which then transmits this via radio to the target location. Conversely, the wireless adapter can receive data via radio and forward it over the fieldbus communication interface to the field device. The supplying of the field device with electrical power then occurs as a rule via an energy supply unit of the wireless adapter.
In the case of autarkic radio field devices and wireless adapters, the communication (for example with a superordinated unit) is, as a rule, conducted via a wireless interface of the radio field device or the wireless adapter. Additionally, such radio field devices or wireless adapters exhibit, as a rule, a hardwired communication interface. The HART standard, for example, provides that the radio field device must, in addition to a wireless interface, also feature a hardwired communication interface. Via such a hardwired communication interface, an on-site configuration of the radio field device or wireless adapter is possible, for example, via a service, or operating, unit (for example a handheld communicator), which is connected to the hardwired communication interface. Furthermore, the hardwired communication interface can be embodied as a fieldbus communication interface, so that the communication is conducted over it according to a bus system, e.g. according to one of the standardized bus systems such as Profibus, Foundation Fieldbus or HART. Through such a fieldbus communication interface, the radio field device or wireless adapter can also be connected to a corresponding hardwired fieldbus.
The energy supply unit or electrical current source of a wireless adapter or a radio field device is normally a disposable battery or a rechargeable battery. It is known to provide the disposable or rechargeable battery with a data storage unit. The static information about the type and characteristics of the disposable or rechargeable battery is stored in the data storage unit. Field devices in stationary or temporary deployment are powered from the disposable or rechargeable battery. The possibility for monitoring the state of the disposable or rechargeable battery is normally provided in the field device.
If the disposable or rechargeable battery is used several times in different field devices, the state of charge, or remaining capacity, of the disposable or rechargeable battery is then unknown. Moreover, the monitoring of the state of the disposable or rechargeable battery is then only possible to a limited degree or not possible at all.